The LLC-PK1 cell line is unique in its ability to actively transport sugar. Its Na+-dependent sugar transport system makes it an excellent model system for sugar reabsorption by the proximal tubule of mammalian kidney. Like other cell lines, this culture is acclaimed as having inherent advantages relative to the tissue to which it relates, such as: homogeneity of cell type; the ability to return at any future date to the same biological material with which a study was performed by simply thawing cells stored in liquid nitrogen; the ability to grow as much material as is required; the ability to work with both cycling and non-cycling cells; the opportunity to utilize genetic techniques on problems of physiological interest. It is this last advantage which this proposal focuses upon, specifically the isolation of two types of LLC-PD1 mutants: 2) a subline defective in active sugar transport; and 1) a subline capable of gluconeogenesis. The first purpose of this selection scheme will be to acquire a mutant sugar transporter to study structure-function relations of the isolated transport proteins. The second long range goal, in which both types of mutants would be involved, is to study the possible interrelationships of active sugar transport and cellular metabolism, specifically renal gluconeogenesis.